This invention relates generally to charge particle beam techniques and devices for solid state device fabrication and more particularly to an ion implantation apparatus that uses an ion source chamber having a uniquely formed interior surface and longer life.
Ion implantation tools are well known to the prior art. Such tools have been and are still used in the production of semiconductor integrated circuits and other solid state devices.
Broadly speaking, these ion implantation tools are designed to generate an ion beam, accelerate it, define it and manipulate it so that the generated ions can be implanted beneath the surface of the device, e.g., the semiconductor substrate, against which the ion beam is directed. The implanted ions are thus used to alter the characteristics of the substrate.
As is well known, in such an apparatus, a selected material is introduced into an ion generation chamber or arc chamber preferably in gaseous form. In this ion generation chamber, using known techniques, the gas is energized and formed into a high density plasma from which ions can be extracted. By using suitable electrostatic and/or magnetic forces, ions of the material are extracted from the plasma, accelerated, focused by a so called charged particle optical system and directed against the surface of the solid state device, in a controlled manner, so that the ions in the beam can be controllably implanted into the solid state device where the implanted ions will create selected characteristics or effects.
More particularly, the formation of the plasma in the ion generation chamber is accomplished by introducing the selected elements or compounds, preferably in a heated gaseous form, into the chamber between a heated filament and a reflector plate and in the presence of a magnetic field. In the chamber the electrons, thermionically emitted from the filament, are further energized and cause to oscillate. These oscillating, energized elections when colliding with the gas particles will to ionize the particles and a plasma is formed. Once the plasma is formed, the positive ions can be extracted therefrom, by an extraction electrode, and formed into a beam.
The reflector and interior walls of these ion generation chambers are highly polished and therefore very smooth. Because the chamber walls are at a temperature lower that of the gaseous materials forming the plasma in the critical stages and in equilibrium states, some of the gaseous material, introduced into the chamber as well as material as well as matter sputtered from the filament will condenses and form solid deposits on the relatively cooler chamber walls. Also it should be noted that the deposition rate may be excessive if there is a change in the pressure of the source feed material which is normally in the range of 2 to 5 xcexcTorr. The polished surface of the chamber walls provides a particularly compliant environment for uniform grain growth of the deposited material. This means that such deposits are usually formed as dendrites. More over because these surfaces are highly polished, as these condensates or deposits get larger and thicker, the high temperature, in the chamber, causes the deposits to peel away from the chamber walls as large flakes. These flakes can drastically shorten the life of the chamber. For example, if a sufficiently large enough flake falls onto the coils of the filament it will reduce the amount of emitted electrons and can cause premature failure of the emitter. If the flakes are even larger, they can short circuit the filament or the reflector to the chamber walls causing a complete collapse of the generated plasma in the chamber.
Such early failures not only interrupt the work schedule, with its attendant costs, but also result in a higher scrap rate in the product being produced. As integrated circuits continue to increase in complexity, it becomes increasingly expensive for manufacturers to continue to suffer such premature failures in their ion implantation equipment. To avoid this problem, manufacturers now shorten their production runs and frequently dismantle the chambers to clean the interior chamber walls of these deposits before they can flake off and damage the equipment.
Therefore, there are compelling economic reasons to avoid early failures in the ion generation chamber due to such flakes. This will not only extend the life of the present ion generation chambers but will also extend the length of the production cycle between the necessary chamber cleaning cycles now required.
It thus becomes desirable that means be found to avoid the flaking problems now found in such ion generation chambers.
The present invention is therefore directed to a unique ion generator or arc chamber for use in an ion implantation apparatus in which the inner surface of the chamber walls is treated to prevent any condensates or deposits of the materials used in the chamber from achieving a size sufficient large enough to adversely affect the operation of the chamber, if the deposits peel of the interior walls of the chamber.
The unique ion generation chamber of the present invention accomplishes this desirable result by providing a roughened, serrated or knurled surface on the interior walls that will prevent deposited materials from growing to a size such that any flakes of such deposits that may separate from the interior walls will not adversely affect the operation of the chamber.
By limiting the size of such flakes, the invention extends the average life of the filaments used in the chamber as well as the average time between cleaning of the inner chamber walls. The present invention thus improves the efficiency of the ion implantation apparatus.
Ion generation chambers having smooth interior surfaces, as taught by the prior art, generally have a useful life of between 160 and 190 hours before the filament burns out, or gets shorted. Actual tests run with an ion generation chamber having roughened interior walls, in accordance with the present invention, were found to have useful lives in excess of 400 hours.
The present invention was particularly efficacious when the germanium based gases are used.
The invention is directed toward an ion implantation apparatus or implanter comprising an ion generation or arc chamber having inwardly facing surfaces with two electrodes in the chamber, an inlet for introducing a feed material to be ionized, an outlet for ionizing the feed material within the chamber wherein the inner surfaces of the chamber have roughened, serrated or knurled surfaces to prevent the feed material to forming flakes large enough to cause short circuits in the chamber.
Therefore, it is an object of the present invention to extend the life of filaments in ion generation chambers.
It is a further object of the invention to eliminate unnecessary cleaning of the interior walls of ion generation chambers.
It is a still further object of the invention to improve the output of ion implantation machines.
These objects, features and advantages of the present invention will become further apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings wherein: